The present invention relates generally to the field of electrosurgery and, more particularly, to surgical devices and methods which employ high frequency voltage to cut and ablate body tissue.
Conventional electrosurgical methods are widely used since they generally reduce patient bleeding associated with tissue cutting operations and improve the surgeon""s visibility. These traditional electrosurgical techniques for treatment have typically relied on thermal methods to rapidly heat and vaporize liquid within tissue and to cause cellular destruction. In conventional monopolar electrosurgery, for example, electric current is directed along a defined path from the exposed or active electrode through the patient""s body to the return electrode, which is externally attached to a suitable location on the patient""s skin. In addition, since the defined path through the patient""s body has a relatively high electrical impedance, large voltage differences must typically be applied between the active and return electrodes to generate a current suitable for cutting or coagulation of the target tissue. This current, however, may inadvertently flow along localized pathways in the body having less impedance than the defined electrical path. This situation will substantially increase the current flowing through these paths, possibly causing damage to or destroying tissue along and surrounding this pathway.
Bipolar electrosurgical devices have an inherent advantage over monopolar devices because the return current path does not flow through the patient beyond the immediate site of application of the bipolar electrodes. In bipolar devices, both the active and return electrode are typically exposed so that they may both contact tissue, thereby providing a return current path from the active to the return electrode through the tissue. One drawback with this configuration, however, is that the return electrode may cause tissue desiccation or destruction at its contact point with the patient""s tissue.
Another limitation of conventional bipolar and monopolar electrosurgery devices is that they are not suitable for the precise removal (i.e., ablation) or tissue. For example, conventional electrosurgical cutting devices typically operate by creating a voltage difference between the active electrode and the target tissue, causing an electrical arc to form across the physical gap between the electrode and tissue. At the point of contact of the electric arcs with tissue, rapid tissue heating occurs due to high current density between the electrode and tissue. This high current density causes cellular fluids to rapidly vaporize into steam, thereby producing a xe2x80x9ccutting effectxe2x80x9d along the pathway of localized tissue heating. The tissue is parted along the pathway of evaporated cellular fluid, inducing undesirable collateral tissue damage in regions surrounding the target tissue site.
The use of electrosurgical procedures (both monopolar and bipolar) in electrically conductive environments can be further problematic. For example, many arthroscopic procedures require flushing of the region to be treated with isotonic saline, both to maintain an isotonic environment and to keep the field of view clear. However, the presence of saline, which is a highly conductive electrolyte, can cause shorting of the active electrode(s) in conventional monopolar and bipolar electrosurgery. Such shorting causes unnecessary heating in the treatment environment and can further cause non-specific tissue destruction.
Present electrosurgical techniques used for tissue ablation also suffer from an inability to control the depth of necrosis in the tissue being treated. Most electrosurgical devices rely on creation of an electric arc between the treating electrode and the tissue being cut or ablated to cause the desired localized heating. Such arcs, however, often create very high temperatures causing a depth of necrosis greater than 500 xcexcm, frequently greater than 800 xcexcm, and sometimes as great as 1700 xcexcm. The inability to control such depth of necrosis is a significant disadvantage in using electrosurgical techniques for tissue ablation, particularly in arthroscopic procedures for ablating and/or reshaping fibrocartilage, articular cartilage, meniscal tissue, and the like.
In an effort to overcome at least some of these limitations of electrosurgery, laser apparatus have been developed for use in arthroscopic and other surgical procedures. Lasers do not suffer from electrical shorting in conductive environments, and certain types of lasers allow for very controlled cutting with limited depth of necrosis. Despite these advantages, laser devices suffer from their own set of deficiencies. In the first place, laser equipment can be very expensive because of the costs associated with the laser light sources. Moreover, those lasers which permit acceptable depths of necrosis (such as excimer lasers, erbium:YAG lasers, and the like) provide a very low volumetric ablation rate, which is a particular disadvantage in cutting and ablation of fibrocartilage, articular cartilage, and meniscal tissue. The holmium:YAG and Nd:YAG lasers provide much higher volumetric ablation rates, but are much less able to control depth of necrosis than are the slower laser devices. The CO2 lasers provide high rate of ablation and low depth of tissue necrosis, but cannot operate in a liquid-filled cavity.
Excimer lasers, which operate in an ultraviolet wavelength, cause photodissociation of human tissue, commonly referred to as cold ablation. Through this mechanism, organic molecules can be disintegrated into light hydrocarbon gases that are removed from the target site. Such photodissociation reduces the likelihood of thermal damage to tissue outside of the target site. Although promising, excimer lasers must be operated in pulses so that ablation plumes created during operation can clear. This prevents excessive secondary heating of the plume of ablation products which can increase the likelihood of collateral tissue damage as well as a decrease in the rate of ablation. Unfortunately, the pulsed mode of operation reduces the volumetric ablation rate, which may increase the time spent in surgery.
The present invention provides systems, apparatus and methods for selectively applying electrical energy to body tissue.
In one embodiment, the method of the present invention comprises positioning an electrosurgical probe or catheter adjacent the target site so one or more active electrode(s) and one or more return electrode(s) are positioned in the region of the body structure. The return electrode(s) are electrically insulated from the active electrode(s) and the patient""s body, and a high frequency voltage difference is applied between the active and return electrode(s) to modify or ablate at least a portion of the body structure.
In a specific configuration, the active and return electrode(s) are spaced from each other on the distal end portion of a surgical instrument. The return electrode(s) are insulated from the active electrode(s) and the patient""s body by an insulator, preferably a thin, insulating jacket that surrounds the shaft of the instrument and the return electrode. In one embodiment, the active electrode(s) are immersed in electrically conductive fluid such that a conductive path is created between the insulator and the active electrode(s). The electrically conductive fluid may be delivered directly to the active electrode(s) or the entire target site may be submersed within the conductive fluid. Applicant believes that the conductive fluid creates a virtual conductor or virtual electrode that includes the active electrode(s) and the conductive fluid surrounding the distal end portion of the instrument. With this configuration, a capacitor is created with the return electrode functioning as the second parallel plate or conductor and the insulator functioning as the dielectric between the conductors. When high frequency voltage is applied between the conductors, a potential difference is created that results in a charge on the conductors, creating an electric field therebetween.
According to the present invention, the active and return electrode(s) are configured such that the charge on the active electrode(s) is sufficient to modify tissue in contact with, or in close proximity to, the active electrode(s). In some embodiments, this charge is sufficient to ablate or volumetrically remove the tissue. Since the current is not flowing into the tissue, this tissue modification or ablation is accomplished at substantially lower temperatures than traditional electrosurgery, which reduces collateral tissue damage. In addition, the current does not penetrate beyond the target tissue site, which further reduces damage to the surrounding and underlying tissue. Moreover, the electric current is precisely controlled, which allows the device to be used adjacent to electrically sensitive structures, such as nerves, the heart or the spine. Another advantage of the present invention is that the alternating current flow between the conductors is more uniform across the surface of the return electrode, rather than collecting at the distal corner of the return electrode as may occur with traditional electrosurgery devices.
In a specific embodiment, a sufficient high frequency voltage is applied between the active and return electrodes to generate a plasma adjacent to the active electrode(s), and to volumetrically remove or ablate at least a portion of the target tissue. The high frequency voltage generates electric fields around the active electrode(s) with sufficient energy to ionize the conductive fluid adjacent to the active electrode(s). Within the ionized gas or plasma, free electrons are accelerated, and electron-atoms collisions liberate more electrons, and the process cascades until the plasma contains sufficient energy to break apart the tissue molecules, causing molecular dissociation and ablation of the target tissue.
In some embodiments, the high frequency voltage applied to the electrode terminal(s) is sufficient to vaporize the electrically conductive fluid (e.g., gel or saline) between the electrode terminal(s) and the tissue. Within the vaporized fluid, an ionized plasma is formed and charged particles (e.g., electrons) are accelerated towards the tissue to cause the molecular breakdown or disintegration of several cell layers of the tissue. This molecular dissociation is accompanied by the volumetric removal of the tissue. The short range of the accelerated charged particles within the plasma layer confines the molecular dissociation process to the surface layer to minimize damage and necrosis to the underlying tissue. This process can be precisely controlled to effect the volumetric removal of tissue as thin as 10 to 150 microns with minimal heating of, or damage to, surrounding or underlying tissue structures. A more complete description of this phenomena is described in commonly assigned U.S. Pat. No. 5,697,882.
In one application, the present invention is particularly useful for selectively contracting soft collagen tissue and other body structures, while limiting thermal damage or molecular dissociation of such tissue and limiting the thermal damage to tissue adjacent to and underlying the treatment site. The systems and methods of the present invention are particularly useful for surgical procedures in electrically conducting environments, such as arthroscopic procedures in the joints, e.g., shoulder, knee, hip, hand, foot, elbow or the like. A more complete description of bipolar methods for shrinking tissue in joints can be found in U.S. patent Ser. No. 09/273,612, the complete disclosure of which is hereby incorporated herein by reference. In this application, the return electrode is provided on the perimeter of the shaft such that the conductive fluid in the joint provides a conductive path between the active and return electrodes. One potential problem with this configuration is that the return electrode may cause burning of tissue near the portal within the joint due to space constraints within the joint, particularly the shoulder capsule. According to the present invention, the return electrode is insulated from the conductive fluid and from the patient""s body to eliminate this potential burning of the tissue. A sufficient high frequency voltage difference can be applied to the active and return electrodes to effect contraction of collagen tissue in the joint without causing molecular dissociation or charring of the tissue.
In another application, the present invention is particularly useful for reducing or eliminating the effects of restenosis in coronary arteries by selectively removing tissue ingrowth in or around stents anchored therein. In this method, an electrosurgical catheter is advanced within the body passage such that an electrode terminal and a return electrode are positioned near the occlusive media. High frequency voltage is applied between the active and return electrodes as described above to produce a charge sufficient to volumetrically remove the occlusive media in situ. In exemplary embodiments, the high frequency voltage is sufficient to effect molecular dissociation or disintegration of the occlusive media, thus converting the solid media into non-condensable gases. According to the present invention, the return electrode is insulated from the active electrode and the patient""s body to eliminate the potential for contact between the return electrode and the body lumen, which could otherwise could thermal damage to the walls of the vessel.
The present invention is particularly useful in a lumen containing a lumenal prosthesis, such as a stent, stent-graft or graft, which may be metallic, non-metallic or a non-metallic coated metallic structure. Restenosis often occurs when arthermateous media or thrombus moves or grows through or around the cylindrical wall of the prosthesis to partially occlude the body passage. In this application, it is particularly useful to insulate the return electrode from the conductive stent, and to control the flow of current at the target site to minimize current flow through the stent.
Apparatus according to the present invention generally include an electrosurgical instrument having a shaft with proximal and distal ends, one or more active electrode(s) at the distal end and one or more connectors coupling the active electrode(s) to a source of high frequency electrical energy. The apparatus further includes one or more return electrode(s) at or near the distal end of the instrument shaft and being electrically insulated from the active electrode(s) and the patient""s body. In some embodiments, the instrument will comprise a catheter designed for percutaneous and/or transluminal delivery. In other embodiments, the instrument will comprise a more rigid probe designed for percutaneous or direct delivery in either open procedures or port access type procedures. In both embodiments, the apparatus will include a high frequency power supply for applying a high frequency voltage to the electrode terminal(s).
In a specific configuration, the instrument comprises one or more active electrode(s) at the distal end, and a return electrode on the instrument shaft and spaced proximally from the active electrode(s). A thin, electrically insulating jacket surrounds the return electrode to insulate the return electrode from the active electrode. The insulating jacket has a material and thickness selected that will allow for sufficient charge to build on the electrodes to ablate or otherwise modify tissue adjacent to the active electrode(s). In the representative embodiment, the insulator comprises a polytetrafluoroethylene, polyimide, teflon, urethane or silicone material, and has a thickness in the range of about 0.01 to 0.5 mm.
In preferred embodiments, the apparatus will further include a supply of electrically conductive fluid and a fluid delivery element for delivering electrically conducting fluid to the electrode terminal(s) and the target site. The fluid delivery element may be located on the instrument, e.g., a fluid lumen or tube, or it may be part of a separate instrument. Alternatively, an electrically conducting gel or spray, such as a saline electrolyte or other conductive gel, may be applied to the target site. In this embodiment, the apparatus may not have a fluid delivery element. In both embodiments, the electrically conducting fluid will preferably generate a current flow path between the active electrode(s) and the portion of the insulator immediately surrounding the return electrode.
The electrosurgical instrument will preferably include an electrically insulating electrode support member, preferably an inorganic support material (e.g., ceramic, glass, glass/ceramic, silicone etc.) having a tissue treatment surface at the distal end of the instrument shaft. One or more electrode terminal(s) are coupled to, or integral with, the electrode support member such that the electrode terminal(s) are spaced from the return electrode. In one embodiment, the instrument includes an electrode array having a plurality of electrically isolated electrode terminals embedded into the electrode support member such that the electrode terminals extend about 0.0 mm to about 10 mm distally from the tissue treatment surface of the electrode support member. In some embodiments, the probe will further include one or more lumens for delivering electrically conductive fluid and/or aspirating the target site to one or more openings around the tissue treatment surface of the electrode support member. In an exemplary embodiment, the lumen will extend through a fluid tube exterior to the probe shaft that ends proximal to the return electrode.